Compact electrostatic discharge (ESD) protection structure

ABSTRACT

A multi-gate Schottky depletion-mode field effect transistor (FET), at least one diode and two resistors comprise a compact electrostatic discharge (ESD) protection structure. This ESD protection structure can be laid out in a smaller area than typical multiple diode ESD devices. The multi-gate FET may comprise various types of high-electron-mobility transistor (HEMT) devices, e.g., (pseudomorphic) pHEMT, (metamorphic) mHEMT, induced HEMT. The multiple gates of the Schottky field effect device are used to form an ESD trigger and charge draining paths for protection of circuits following the ESD protection device. Both single and dual polarity ESD protection devices may be provided on an integrated circuit die for protection of input-output circuits thereof.

RELATED PATENT APPLICATION

This application is a Divisional of U.S. patent application Ser. No.14/267,185, filed May 1, 2014, now U.S. Pat. No. 9,431,390 issued Aug.30, 2016, which claims priority to commonly owned U.S. ProvisionalPatent Application No. 61/819,252, filed May 3, 2013; and are bothhereby incorporated by reference herein for all purposes.

TECHNICAL FIELD

The present disclosure relates to a semiconductor protection structures,in particular electrostatic discharge (ESD) protection structures.

BACKGROUND

A Schottky gate depletion-mode field effect device is sensitive to ESDdamage due to its delicate metallic gate structure (0.5 μm or smallermetal gate length). Unlike CMOS silicon or bipolar transistor processes,there is no robust P-N junction diode available in ahigh-electron-mobility transistor (HEMT) process to form a compact ESDprotection diode. A HEMT, also known as heterostructure FET (HFET) ormodulation-doped FET (MODFET), is a field-effect transistorincorporating a junction between two materials with different band gaps(i.e., a heterojunction) as the channel instead of a doped region (as isgenerally the case for MOSFET). There are several versions of the HEMT,e.g., pseudomorphic HEMT (pHEMT), metamorphic HEMT (mHEMT), inducedHEMT, etc. Several large Schottky diodes formed with the gate of thepHEMT device have to be cascaded in series to adequately protect theactive HEMT circuits. These multiple Schottky diodes consume a largearea in an expensive GaAs integrated circuit die.

A Schottky diode, also known as a hot carrier diode, is a semiconductordiode which has a low forward voltage drop and a very fast switchingaction. There is a small voltage drop across the diode terminals whencurrent flows through a diode. A normal diode will have a voltage dropbetween 0.6 to 1.7 volts, while a Schottky diode voltage drop is usuallybetween 0.15 and 0.45 volts. This lower voltage drop provides bettersystem efficiency and higher switching speed. In a Schottky diode, asemiconductor-metal junction is formed between a semiconductor and ametal, thus creating a Schottky barrier. An N-type semiconductor acts asthe cathode and the metal side acts as the anode of the Schottky diode.This Schottky barrier results in both a low forward voltage drop andvery fast switching. ESD protection can be provided by cascading severallarge Schottky diodes. Due to the Schottky diode's low turn on voltage,several stacked diodes are required to handle the operating voltage, anda large area is required to handle the current. Thus using a Schottkydiode configuration requires a large die area.

SUMMARY

Therefore a need exists for an efficient and compact ESD protectionstructure compatible with HEMT and other semiconductor devices that doesnot require using Schottky diodes.

According to an embodiment, an electrostatic discharge (ESD) protectiondevice may comprise: a field effect transistor (FET) having a drain, atleast two gates and a source, wherein the drain thereof may be coupledto a node of a circuit to be protected from an ESD event; at least onediode coupled between the source of the FET and a power supply common; afirst resistor coupled between the at least two gates of the FET; and asecond resistor coupled to a one of the at least two gates and the powersupply common.

According to a further embodiment, one of the at least two gates may bea trigger gate and another one of the at least two gates may be adischarge gate. According to a further embodiment, the FET may be adepletion-mode FET. According to a further embodiment, the at least onediode may be two diodes connected in series between the source of theFET and power supply common. According to a further embodiment, thepower supply common may be coupled to an electrical ground According toa further embodiment, the depletion-mode FET may be ahigh-electron-mobility transistor (HEMT). According to a furtherembodiment, the HEMT may be a pseudomorphic HEMT (pHEMT). According to afurther embodiment, the HEMT may be a metamorphic HEMT (mHEMT).According to a further embodiment, the HEMT may be an induced HEMT.

According to a further embodiment, the FET, the at least one diode andthe first and second resistors may be fabricated on an integratedcircuit die and coupled to the circuit node that may be coupled to anexternal connection of the integrated circuit die. According to afurther embodiment, a function of the external connection of theintegrated circuit die may be selected from the group consisting of ananalog input, a digital input, an analog output, a digital output, ananalog input/output, a digital input/output, a power connection, a biasinput, and an external compensation capacitor.

According to another embodiment, an electrostatic discharge (ESD)protection device may comprise: a first field effect transistor (FET)having a drain, at least two gates and a source, wherein the drainthereof may be coupled to a node of a circuit to be protected from anESD event; at least one first diode having an anode coupled to thesource of the first FET; a first resistor coupled between the at leasttwo gates of the first FET; and a second resistor coupled to a one ofthe at least two gates and a cathode of the at least one first diode; asecond field effect transistor (FET) having a drain, at least two gatesand a source, wherein the drain thereof may be coupled to a power supplycommon; at least one second diode having an cathode coupled to thecathode of the at least one first diode; a third resistor coupledbetween the at least two gates of the second FET; and a fourth resistorcoupled to a one of the at least two gates of second FET and a cathodeof the at least one second diode.

According to a further embodiment, one of the at least two gates of thefirst and second FETs may be trigger gates and another one of the atleast two gates of the first and second FETs may be discharge gates.According to a further embodiment, the first and second FETs may bedepletion-mode FETs. According to a further embodiment, the at least onefirst and second diodes may be two diodes each connected in seriesbetween the sources of the first and second FETs. According to a furtherembodiment, the power supply common may be coupled to an electricalground. According to a further embodiment, the first and seconddepletion-mode FETs may be high-electron-mobility transistors (HEMTs).According to a further embodiment, the HEMTs may be selected from thegroup consisting of pseudomorphic HEMTs (pHEMTs), metamorphic HEMTs(mHEMTs) and induced HEMTs.

According to a further embodiment, the first and second FETs, the atleast one first and second diodes and the first, second, third andfourth resistors may be fabricated on an integrated circuit die andcoupled to the circuit node that may be coupled to an externalconnection of the integrated circuit die. According to a furtherembodiment, a function of the external connection of the integratedcircuit die may comprise a radio frequency signal input. According to afurther embodiment, a function of the external connection of theintegrated circuit die may comprise a radio frequency signal output.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present disclosure may be acquiredby referring to the following description taken in conjunction with theaccompanying drawings wherein:

FIG. 1 illustrates a schematic isometric cross section diagram of a HEMTdevice, according to the teachings of this disclosure;

FIG. 2 illustrates a schematic diagram of a prior technology singlepolarity depletion-mode FET ESD protection device for direct current(DC) and control ports;

FIG. 3 illustrates a schematic diagram of a single polarity multi-gateSchottky depletion-mode FET ESD protection device for direct current(DC) and control ports, according to a specific example embodiment ofthis disclosure;

FIG. 4 illustrates a schematic plan view of a prior technology structurefor the ESD protection device shown in FIG. 2;

FIG. 5 illustrates a schematic plan view of a structure for the ESDprotection device shown in FIG. 3, according to a specific exampleembodiment of this disclosure;

FIG. 6 illustrates a more detailed schematic plan view of a structurefor the ESD protection device shown in FIG. 3, according to a specificexample embodiment of this disclosure;

FIG. 7 illustrates a schematic diagram of a dual polarity multi-gateSchottky depletion-mode FET ESD protection device for radio frequency(RF) ports, according to another specific example embodiment of thisdisclosure; and

FIGS. 8 and 8A illustrate a schematic plan view of a structure for theESD protection device shown in FIG. 7, according to a specific exampleembodiment of this disclosure.

While the present disclosure is susceptible to various modifications andalternative forms, specific example embodiments thereof have been shownin the drawings and are herein described in detail. It should beunderstood, however, that the description herein of specific exampleembodiments is not intended to limit the disclosure to the particularforms disclosed herein, but on the contrary, this disclosure is to coverall modifications and equivalents as defined by the appended claims.

DETAILED DESCRIPTION

According to various embodiments, a pseudomorphic high electron mobilitytransistor (pHEMT), also known as heterostructure FET ormodulation-doped FET is used as an example herein to describe theconcept of a compact ESD protection device according to variousembodiments disclosed herein. Heretofore, several large Schottky diodeshad to be formed with the gate of a pHEMT device and cascaded in seriesto increase the voltage and adequately protect the active circuits.These multiple diode devices consumed a large area in an expensive GaAsintegrated circuit die. According to various embodiments of thisdisclosure, it is proposed to use a multiple-gate HEMT to form a compactESD protection device. The multiple-gates of the HEMT device may be usedto form ESD trigger and charge draining paths for protection of circuitsfollowing the ESD protection devices and structures. The ESD protectiondevice structure can be laid out in a much smaller area than themultiple diode ESD device structure. It is contemplated and within thescope of this disclosure that various types of HEMT devices, e.g.,pHEMT, mHEMT, induced HEMT, etc., may be used with the ESD protectiondevices disclosed herein.

Referring now to the drawings, the details of example embodiments areschematically illustrated. Like elements in the drawings will berepresented by like numbers, and similar elements will be represented bylike numbers with a different lower case letter suffix.

Referring to FIG. 1, depicted is a schematic isometric cross sectiondiagram of a HEMT device, according to the teachings of this disclosure.A pHEMT is shown for illustrative purposes, but it is contemplated andwithin the scope of this invention that other HEMT devices may besimilarly used according to the teachings of this disclosure. The HEMTdevice may comprise a substrate 112, a two dimensional electron gaslayer 110, a spacer 108, a barrier 106, a capping layer 104, and metaldrain, source and gate electrodes 102. The source, gate and drain metal102 may comprise, but is not limited to, gold. The barrier 106 maycomprise, but is not limited to, aluminum gallium arsenide (AlGaAs). Thespacer 108 may comprise, but is not limited to, gallium arsenide (GaAs).The two dimensional electron gas layer 110 may comprise, but is notlimited to, indium gallium arsenide (InGaAs). The substrate maycomprise, but is not limited to, high resistivity GaAs. The firstresistor 210 may have a resistance value of from about 500 ohms to about2000 ohms. The second resistor 212 may have a resistance value of about2000 ohms.

Referring to FIGS. 2 and 4, depicted are a schematic diagram of a priortechnology single polarity depletion-mode FET ESD protection device fordirect current (DC) and control ports, and a schematic plan view of theprior technology structure for the ESD protection device shown in FIG.2. A single polarity single-gate ESD protection device 202 has been usedto protect control signal and/or bias supply nodes (pins) of circuits206 of an integrated circuit package (not shown). The ESD protectiondevice 202 may comprise a field effect transistor (FET) 208 having adrain (D), a source (S) and a single gate (G); first and second Schottkydiodes 214 and 216, a third diode 218, and first and second gateresistors 210 and 212. The third diode 218 is a trigger diode thatconducts (goes into avalanche breakdown) when an ESD event occurs,thereby turning on the transistor 208. The Schottky diodes 214 and 216are used for voltage level shifting to prevent the depletion modetransistor 208 from turning on and conducting current during normaloperation.

Referring to FIGS. 3, 5 and 6, depicted are a schematic diagram of asingle polarity multi-gate Schottky depletion-mode FET ESD protectiondevice for direct current (DC) and control ports, and schematic planviews of a structure for the ESD protection device shown in FIG. 3,according to a specific example embodiment of this disclosure. A singlepolarity ESD protection device 302 having Schottky multi-gates may beused to protect control signal and/or bias supply nodes (pins) ofcircuits 306 of an integrated circuit package (not shown). The ESDprotection device 302 may comprise a multi-gate Schottky depletion-modefield effect transistor (FET) 308, e.g., HEMT device, having a drain(D), a source (S), first and second trigger gates (G1 and G2), first andsecond diodes 314 and 316, and first and second gate resistors 310 and312. It is contemplated and within the scope of this disclosure that theFET 308 may have two or more gates. At least one level shifting diodemay be coupled between the source of the FET 308 and a power supplycommon, e.g., an electrical ground. The drain of the FET 308 may becoupled to a node 304 that may be coupled to an external connection(pin) of an integrated circuit (IC) package (not shown). The externalconnection (pin) of the IC package may be used as, for example but notlimited to, an analog input, a digital input, an analog output, adigital output, an analog input/output, a digital input/output, a powerconnection, a bias input, an external compensation capacitor, etc.

When negative electrostatic charges accumulate at node 304 the secondtrigger gate (G2) will be forward biased and drain these charges toground through the second gate resistor 312. When positive electrostaticcharges accumulate at the node 304, a positive potential will be builtup until the first trigger gate (G1) is in reverse breakdown. Thisbreakdown current will flow to ground and establish a positive potentialacross the second gate resistor 312. Thus providing sufficient voltageto turn on FET 308 with the second gate G2 thereof when thegate-to-source potential is more positive than the turn-on voltage ofthe series connected first and second diodes 314 and 316. These firstand second diodes 314 and 316 are coupled between the source of the FET308 and a power supply common, e.g., ground, and provide voltage levelshifting to prevent a depletion mode transistor from turning on(conducting). The drain current of the FET 308 provides another path todissipate the positive electrostatic charges at the node 304 and helpsto prevent the first trigger gate G1 from having excessive breakdowncurrent that may damage the first trigger gate G1.

Hence, a multi-gate structure FET 308 is a unique way to combine atrigger diode device and a discharge gate FET that saves preciousintegrated circuit die area. In addition, only three active device areasare necessary for the single polarity multiple-gate ESD protectiondevice 302: 1) FET 308, 2) and 3) first and second diodes 314 and 316.The prior technology ESD protection device 202 requires four activedevice areas 1) FET 208, 2) trigger third diode 218, 3) and 4) levelshifting diodes 214 and 216. Therefore, the prior technology ESDprotection device 202 requires a larger active device area on theintegrated circuit die (not shown) than does the single polaritymultiple-gate ESD protection device 302 to achieve the same ESDprotection level, according to the teachings of this disclosure.

Referring to FIGS. 7, 8 and 8A, depicted are a schematic diagram of adual polarity multi-gate Schottky depletion-mode FET ESD protectiondevice for radio frequency (RF) ports, and a schematic plan view of astructure for the ESD protection device shown in FIG. 7, according toanother specific example embodiment of this disclosure. A dual polaritymulti-gate Schottky depletion-mode FET ESD protection device 702 may beused to protect control, signal and/or bias supply nodes (pins) ofcircuits 706 of an integrated circuit package (not shown). The ESDprotection device 702 may comprise a first HEMT device 308 having adrain, a source and first and second gates (G1 and G2); first and seconddiodes 314 and 316, first and second gate resistors 310 and 312, asecond HEMT device 708 having a drain, a source and first and secondgates (G1 and G2); third and fourth diodes 714 and 716, third and fourthgate resistors 710 and 712. The ESD protection device 702 mayadvantageously be used with RF ports that are associated with high RFpower devices. This ESD protection circuit may be used in the presenceof large positive and negative RF voltage swings. The working principleof this dual polarity multi-gate FET ESD protection device 702 issubstantially similar to that of the single polarity multi-gate ESDprotection device 308. Elements 708-716 function as a mirror image ofthe elements 308-316.

While embodiments of this disclosure have been depicted, described, andare defined by reference to example embodiments of the disclosure, suchreferences do not imply a limitation on the disclosure, and no suchlimitation is to be inferred. The subject matter disclosed is capable ofconsiderable modification, alteration, and equivalents in form andfunction, as will occur to those ordinarily skilled in the pertinent artand having the benefit of this disclosure. The depicted and describedembodiments of this disclosure are examples only, and are not exhaustiveof the scope of the disclosure.

What is claimed is:
 1. An electrostatic discharge (ESD) protectiondevice, comprising: a first field effect transistor (FET) having adrain, at least two gates and a source, wherein the drain thereof iscoupled to a node of a circuit to be protected from an ESD event; atleast one first diode having an anode coupled to the source of the firstFET; a first resistor coupled between the at least two gates of thefirst FET; and a second resistor coupled to a one of the at least twogates and a cathode of the at least one first diode; a second fieldeffect transistor (FET) having a drain, at least two gates and a source,wherein the drain thereof is coupled to a power supply common; at leastone second diode having an cathode coupled to the cathode of the atleast one first diode; a third resistor coupled between the at least twogates of the second FET; and a fourth resistor coupled to a one of theat least two gates of second FET and a cathode of the at least onesecond diode.
 2. The ESD protection device according to claim 1, whereinone of the at least two gates of the first and second FETs are triggergates and another one of the at least two gates of the first and secondFETs are discharge gates.
 3. The ESD protection device according toclaim 1, wherein the at least one first and second diodes are two diodeseach connected in series between the sources of the first and secondFETs.
 4. The ESD protection device according to claim 1, wherein thepower supply common is coupled to an electrical ground.
 5. The ESDprotection device according to claim 1, wherein the first and secondFETs are depletion-mode FETs.
 6. The ESD protection device according toclaim 5, wherein the first and second depletion-mode FETs arehigh-electron-mobility transistors (HEMTs).
 7. The ESD protection deviceaccording to claim 6, wherein the HEMTs are selected from the groupconsisting of pseudomorphic HEMTs (pHEMTs), metamorphic HEMTs (mHEMTs)and induced HEMTs.
 8. The ESD protection device according to claim 1,wherein the first and second FETs, the at least one first and seconddiodes and the first, second, third and fourth resistors are fabricatedon an integrated circuit die and coupled to the circuit node that iscoupled to an external connection of the integrated circuit die.
 9. TheESD protection device according to claim 8, wherein a function of theexternal connection of the integrated circuit die comprises a radiofrequency signal input.
 10. The ESD protection device according to claim8, wherein a function of the external connection of the integratedcircuit die comprises a radio frequency signal output.
 11. Anelectrostatic discharge (ESD) protection device, comprising: a firstfield effect transistor (FET) having a drain, at least two gates and asource, wherein the drain thereof is coupled to a node of a circuit tobe protected from an ESD event; a first and second in series connecteddiodes, wherein an anode of the first and second in series connecteddiodes is coupled to the source of the first FET; a first resistorcoupled between the at least two gates of the first FET; and a secondresistor coupled to a one of the at least two gates and a cathode of thefirst and second in series connected diodes; a second field effecttransistor (FET) having a drain, at least two gates and a source,wherein the drain thereof is coupled to a power supply common; a thirdand fourth in series connected diodes, wherein a cathode of the thirdand fourth in series connected diodes is coupled to the cathode of thefirst and second in series connected diodes; a third resistor coupledbetween the at least two gates of the second FET; and a fourth resistorcoupled to a one of the at least two gates of second FET and the cathodeof the third and fourth in series connected diodes.
 12. The ESDprotection device according to claim 11, wherein one of the at least twogates of the first and second FETs are trigger gates and another one ofthe at least two gates of the first and second FETs are discharge gates.13. The ESD protection device according to claim 11, wherein the powersupply common is coupled to an electrical ground.
 14. The ESD protectiondevice according to claim 11, wherein the first and second FETs aredepletion-mode FETs.
 15. The ESD protection device according to claim14, wherein the first and second depletion-mode FETs arehigh-electron-mobility transistors (HEMTs).
 16. The ESD protectiondevice according to claim 15, wherein the HEMTs are selected from thegroup consisting of pseudomorphic HEMTs (pHEMTs), metamorphic HEMTs(mHEMTs) and induced HEMTs.
 17. The ESD protection device according toclaim 11, wherein the first and second FETs, the at least one first andsecond diodes and the first, second, third and fourth resistors arefabricated on an integrated circuit die and coupled to the circuit nodethat is coupled to an external connection of the integrated circuit die.18. The ESD protection device according to claim 17, wherein a functionof the external connection of the integrated circuit die comprises aradio frequency signal input.
 19. The ESD protection device according toclaim 18, wherein a function of the external connection of theintegrated circuit die comprises a radio frequency signal output.